sudo du -hxs /And wait patiently... That will summarize everything under / that is on the same file-system as a total size (i.e. not mounted from a different disk, or the tmpfs filesystems). x keeps it on the / file-system, and s gives you the summary, rather than each file or directory listed.

/home/camera (or cameras; going from memory here) will have videos and such of motion events, those can consume a lot of space.

I mounted a NAS under /mnt/ where i backupped my data each night.And apparantly the mounting went somewhere invalid. It was correct for several months, and suddently it was a local folder? So the backups were made locally.

But in the meantime, my linuxmce crashed completely. When i tried to boot, he tried to go into 'maintenance shell'. But didn't succeed. Prob because the disk is full?So 'ive connected the disk to another system and i'm cleaning out the folder /mnt/ for the moment.And i really hope that it'll start properly later on...